Lactase or beta-galactosidase (EC: 3.2.1.23) is an enzyme, which can convert lactose (disaccharides) into the monosaccharides glucose and galactose. Lactose is present in dairy products and more particularly in milk, skimmed milk, cream and other milk products. The breakdown of lactose occurs in the intestinal wall of the human body (and in other mammals) by the natural presence of lactase.
Many humans (and other mammals) suffer from lactose-intolerance, wherein lactase is absent or partially absent in their digestive system. In case where lactose is part of the food or feed, decreased digestion of lactose may lead to intestinal trouble.
Nowadays lactase is added to milk to breakdown the lactose present. Lactase may be added to milk either before or after pasteurisation or sterilization. In general lactase will be inactivated during pasteurisation or sterilization treatment. When lactase is added before sterilization a large amount of lactase may be required in order to reduce the storage time between addition and pasteurisation/sterilization. Although lactase is an active enzyme one has to keep in mind that milk is processed and stored generally at temperatures between 0 and 8° C.
The other possibility is the addition of the enzyme after pasteurisation or sterilization of the milk and before packing. In this case lactase may be added in a lower amount, as it may be at least 10 to 24 hours before the milk is consumed. The enzyme can digest lactose, which may be present during transport and storage in the factory, shop and in the refrigerator of the consumer.
There are several ways to sterilize lactase, for example by chemical and/or heat treatment. However, because of its application in food or feed, sterile filtration is a preferred option.
In the journal Voedingsmiddelentechnologie 13 (1980), 23, a method, which is also described in British patent specification 1477087, is further illustrated. Lactase, usually used by the dairy processing industry as an aqueous solution to which one or more stabilizing agents, such as glycerol, can be added, is filtered before use. The filtered enzyme solution is pumped through a sterile filter then injected via a dosing device into a production line of previously sterilized or pasteurised milk and then mixed with the milk which is subsequently packed under aseptic conditions in uniform packs.
However, in practice, the sterile filter often blocks due to degraded protein, poly- and oligosaccharides remaining in the enzyme solution despite filtering. According to EP 145092, such degradation generally increases the longer the enzyme is stored prior use and may be promoted by the considerable period of time between the production of the enzyme and its use in the dairy processing industry. The repeated cleaning or replacement of the sterile filters is not an option since stopping the whole process requires sterilisation before starting again.
EP 145092 describes a process for the sterile filtration of lactase within 14 days of it being produced. EP 145092 describes that lactase should be sterile filtered after recovery and purification of lactase produced by fermentation, but before the formation of degradation products which are sufficient to clog the sterile filter. However the approach of sterile filtering freshly produced lactase solution does not fulfil the need of lactase solution which can be filtered in-line and which can be added to the sterilized/pasteurised milk. The lactase described in EP 145092 is derived from the yeast Kluyveromyces that is used widely in the dairy industry. The polysaccharides are probably parts of host cell walls, which are formed during the recovery process.